1. Technical Field
The present invention relates to an image sensor and an optical touch system comprising the same.
2. Related Art
In an optical touch screen system, the method of calculating the position of an object is to use an image sensor to generate a picture, analyzing the location of an object image in the picture, calculating the coordinates of the object according to the location of the object image in the picture and a portion of geometric dimensions of the optical touch screen system.
U.S. Pat. No. 4,782,328 discloses an optical touch screen system, which comprises two image sensors configured to capture the image of an object on a touch screen. A processor is coupled with the two image sensors for processing the images from the two image sensors in order to decide sensing paths respectively connecting the object and the two image sensors, and further calculates the coordinates of the object using the sensing paths.
U.S. Pat. No. 7,689,381 B2 discloses another optical touch screen system, which comprises a mirror, two light sources, an image sensor, and a processor. The mirror and the two light sources are disposed at the border of a touch area. The mirror can generate a reflection of an object. The image sensor can capture an image of the object and an image of the reflection. The processor can determine sensing paths passing through the image of the object and the image of the reflection, and then determine the coordinates of the object by the two sensing paths.
Usually, in an optical touch screen system, it is difficult to have uniform background light. In order to precisely determine an object image, the influence of non-uniform background illumination has to be eliminated before the analysis of the object image. A general method is to store a to background picture in advance, subtracting the background picture from a captured picture, and then lastly analyzing the subtracted picture to determine the object image. To perform the aforementioned method, an optical touch screen system always has to store a background picture, which needs a large memory space for storage. Further, the background illumination may change so that the background picture has to be frequently updated, which increases the operation loadings on the optical touch screen system. In addition, the computing procedures of subtracting a background picture from a picture, analyzing the boundary positions of the object image in the subtracted picture, and calculating the coordinates of the object according to the boundary positions consumes a large amount of electrical energy. Furthermore, the optical touch screen system needs a faster clock to be more responsive.